The present invention relates to a structure in the form of a grid or grate (hereinafter "grid") and, more particularly, a grid structure for disposition over trickling filter systems, large air conditioning systems, or heat exchange systems, such as in cooling towers, to provide a platform for a person to walk on without the platform or underlying support media collapsing under the weight of the person.
Trickling filters and cooling tower heat exchange systems typically are structures having a large footprint such that components within the systems cannot be reached from the sides. Therefore, it is necessary for replacement, maintenance or repair for a person or persons to have some structure which allows workers to reach the center of the systems. Sometimes, permanent catwalks are built, but these are expensive and must be custom designed for each installation. Therefore, this solution has not been desirable.
These types of systems typically include a housing in which are located a large number of thin plastic plates aligned in a parallel relationship. In trickling filters, the plates act as support for desired bacteria which form biological filters for water or other liquid flowing through the plates. In air conditioning or other heat exchange systems, the plates act as gas-liquid contact bodies to provide for evaporative heat exchange. The plates are referred to in these industries as "media". The plates are rather thin, on the order of a couple of millimeters or less, and typically have their upper edges exposed to the environment. If a worker were to walk on top of the plates, it is likely that the upper edges of the plates would become broken or bent, which adversely affects the performance of the trickling filter, heat exchanger or other equipment.
Grids forming walking platforms for trickling filters, air conditioning and other air handling systems are known. The grids are in the form of plastic structures which can be placed on top of the media and are intended to distribute the weight of a worker or workers over many of the media plates so that the upper edges of the media are not harmed. Some of the grids presently used have a structure including horizontal flanges extending only along the top surface where the horizontal flanges provide some structural integrity and greater surface area than if such flanges were not used. However, such present injection molded grid structures do not have horizontal flanges on portions of both their upper and lower surfaces, and therefore, the non-flanged surface results in such grids having less structural integrity and have the potential of being crushed under the weight of the person walking on top of them. Due to the molding or thermoforming techniques used to make the present grid structures, horizontal flanges cannot practically be formed on both the lower and upper surfaces and, if increased structural integrity is desired, the grid has to be made using thicker walls. This, of course, requires more material to be used, increasing the cost and weight of the grid.
There is a need for a grid to have the sufficient strength to withstand a compressive force equivalent to the weight of a maintenance person without destroying the integrity of the grid itself, while also providing a safe and comfortable walking surface. The present invention satisfies this need.
In addition to a primary use of the grid structure of the present invention as a platform for performing maintenance, repair and replacement in trickling filters and heat exchange systems, when the grid structure of the present invention is laid upon the top of the media in such systems, the grid acts to shade the media and reduce the degradative effects of UV light. The grid also acts to protect the upper surface of the media from the effects of environment such as hail and heavy rain by acting as a type of deflector shield or splash guard. This is particularly helpful in the case of trickling filters, where heavy rain can wash away part of the biological layer formed on the media. The grid also protects the biological layer in trickling filters and the media in trickling filters and evaporative heat exchanges from the impact and erosive effects of the hydraulic force generated by the liquid distribution system, such as nozzles, a distributor arm, or the like.
The molding techniques of the present invention make it practical to form the grid structure having flanges on opposite surfaces as discussed hereinafter.